They’re called thorns. Introduce a mare in season to a rathorn stallion and, if he doesn’t kill her, eleven months later you get the blackest, meanest little filly you can imagine. All they lack is their sire’s armor.
– Harn, The Sea of Time, "Chapter VI: Challenges", VI
Thorns are cross breeds between a horse mare and rathorn stallion. They've got the vicious nature of rathorns, but not their ivory armor. The Karnids like riding them.
↑The Sea of Time, "Chapter XIII: Dreams and Nightmares", VI — "In their wake, riders on black thorns swept in from all sides. Tori watched as the charge crashed into one circle, rupturing it. The thorns screamed, bit, and kicked, savaging their way in among the Kencyr, barely under their riders’ control."
↑The Sea of Time, "Chapter XXIII: The Feast of Fools", I — "Death’s-head, following him, almost ran into a wall of rearing, lunging thorns. Jame saw that the black mares surrounded them in a circle, around which the Karnids streamed to throw themselves against the front rank of cadets."